Electrode and method used for iontophoresis

ABSTRACT

An iontophoretic electrode has a plurality of ion transmitters for establishing electric field lines in an area and a plurality of receivers for accepting ions flowing along the field lines. A plurality of shields are located to resist ion flow between adjacent transmitters and receivers. The transmitters, shields and receivers are in at least a sequence of transmitter, shield, receiver, shield. The electric field lines emanate substantially in one direction and return in substantially the opposite direction. The transmitters and receivers have matrix structures with space to contain ionic medication and electrolyte, respectively. A support for holding a plurality of sequences has current carrying contacts exposed to connect the transmitters and receivers in circuit with a source of electrical power. The preferred method includes establishing an electric field with lines of energy between a plurality of first and second conductors of ions and then passing ions along the energy lines between the conductors. Thereafter the method includes restricting the flow of ions to paths between adjacent first and second conductors and then positioning the first conductors relative to the second conductors so that the energy lines emanate from the first substantially in one direction return to adjacent second conductors in the opposite direction.

This is a division of application Ser. No. 412,056, filed Sep. 25, 1989,now U.S. Pat. No. 4,950,220.

BACKGROUND OF THE INVENTION Field of the Invention

This invention relates to an apparatus for an electrode and method usedfor iontophoresis, and more specifically, to an electrode and method foruse of the electrode for iontophoretic transport of an ionic substancetransdermally.

Background

Electrodes have been proposed for use in the transdermal delivery ofionic substances. Electromotive force used with an electrode offers theadvantage of controlling the rate of delivery. Skin irritation problemsoccur such as burns at the surface of the skin due to acids or basesformed by electrolysis of the water based medication or electrolyte.Efforts to minimize irritation have been directed to regulating thelevel of current, improving the electrical connection of the electrodewith the skin and reducing the hydrolysis of the water used in the ionicmedication and the electrolyte.

Electrode structures for transdermal drug delivery have an activeelectrode which delivers the ionic medication and an indifferentelectrode with an electrolyte. The active and indifferent electrodes areconnected to the skin forming a circuit. The current passes from a powersource through one of the electrodes to the skin, through the the skininto the subdermal tissue, back out through the skin at a separatelocation and then through the other electrode. Regulation of the rat ofdrug delivery has been controlled by the amount of current flow and thathas been limited by the electrical resistance or impedance of skin. Skinirritation is directly related to the aggressiveness of the ionicsubstances at the interface between the electrode and the skin and theelectrical power needed to deliver the medication. The desired deliveryrate often cannot be tolerated. Various power sources and electrodearrangements and constructions have been suggested to avoid burns andirritation where the iontophoresis takes place.

The efforts to use voltage levels below that required for hydrolysis asin U.S. Pat. No. 4,752,285 or the use of alternating current toeliminate galvanic action are not entirely effective. The ability todeliver the preferred level of medication without skin irritation is afunction of many factors which influence the efficiency with which anymedication can be iontopheretically delivered at a preferred rate. Inthe past the configuration of the electrode has not been considered afactor although various electrode configurations have been proposed.

In U.S. Pat. No. 617,543 a hollow roller electrode of any suitable crosssection with wooden insulating strips between metallic conducting stripsthat are alternately connected to opposite sides of a source ofelectricity. No specific recognition of iontophoresis or disclosure ofcontact by more than one set of metallic strips with the skin tocomplete at one time more than one circuit through the skin aredisclosed. Exit valves dispense medication, surround the surface of thehollow electrode which contains the medication and open when in contactwith the skin.

Batteries are frequently used as a power source because of theirportability and since low voltage direct current is effective. In U.S.Pat. Nos. 222,276 and 770,014 electrode battery combinations areexplained. Battery current drives medication or a conducting salt intothe body. Zinc and copper electrodes form the battery and in the '276patent the electrodes are concentric to one another; in the '014 patentthe electrodes are of similar construction with surfaces which projectthrough separating insulation. The projections may carry absorbentliquid containing pads placed between the projections and the body.

Supports for the electrodes and the power source have also includedreservoirs for the ionic medication. The particular configuration of thesupport is a function of how much of the iontophoretic apparatus iscarried in one package.

U.S. Pat. Nos. 4,164,226 and 4,211,222 disclose a plurality of alternateelectrode elements which are claimed to avoid iontophoretic burn bypermitting current to be applied over a period of time. The '226 patenthas small positive and negative electrodes which are spaciallyintermingled. The size of the positive electrodes may be the same as thenegative or may be larger. A thick porous and preferably moist materialis used between the negative electrode and the skin to eliminateiontophoretic burn by preventing the migration of particles from themetallic electrode as the current passes into the skin.

Electrode structures wherein the active and the indifferent electrodesare carried on an insulator separate from each other but in position tocontact the skin have taken many forms. U.S. Pat. No. 4,325,367 has anelectrode support structure on which is mounted a pair of electrodes inproximity to one another and a source of electrical power for theelectrodes. U.S. Pat. No. 4,406,658 shows an iontophoresis device withan active electrode from which the ionic substance is driven into thebody and an indifferent or ground electrode used to complete theelectrical circuit through the body. The ionic substance can bepositively or negatively charged but the active electrode must also bepositively or negatively charged, respectively. The electrodes in U.S.Pat. No. 4,406,658 are adhesive so as to adhere to the skin. Theelectrodes are held on a support and spaced apart by a projectionbetween them. A battery is also carried in the support and a switch forreversing the polarity of the power supply to the electrodes.

U.S. Pat. No. 4,622,031 has multilayer electrode with a peripheralcontact lip as one electrode element surrounding the other electrodeelement. Current from a battery in that multilayer package drives theions from the reservoir into the skin; a LED indicates current flowthrough the lip and into the skin by means of electrical connection tothe skin with a conductive adhesive. U.S. Pat. No. 4,640,689 discloses apair of side by side active and indifferent electrodes. At least twoelectrode elements are within a cover partially enclosing a reservoirwhich is in one of the elements. A semi permeable member in one elementforms a drug gradient when power is applied from the source through aconductive adhesive to the skin.

Many materials have been suggested and used as conductive electrodesincluding metallic and porous natural and polymer structures dependingupon what drug is desired to be delivered. U.S. Pat. No. 4,708,716discloses a plurality of cells or reservoir units with flexibleseparations therebetween to provide flexibility of the electrode toconform to the contours of the body. Each cell or unit is surrounded bya nonconductive gel. U.S. Pat. No. 4,713,050 has a layered electrodeconstruction with a reservoir having a cover, lip and adhesive. U.S.Pat. No. 4,731,926 discloses a method of manufacture of a multireservoir device which is layered and lipped in configuration. Themethod of making the reservoirs includes occluding foam to provideinsulators between the reservoirs/elements.

U.S. Pat. No. 4,734,090 discloses techniques recognizing the principlethat the sweat ducts have less resistance to the flow of current andtherefore ions so as to direct the current to the stratum corneum or tocircumvent the stratum corneum or by using a system which plugs theentrances to the ducts. U.S. Pat. No. 4,653,501 shows a electrodeconstruction wherein the metal conductor can be reused and the electrodepad can be replaced such that the more expensive part of the electrodeis retained and the body contact part of the electrode is disposable.U.S. Pat. No. 4,416,274 shows an electrode for iontophoresis which hasstructure to inhibit the migration of ions laterally or in a directionparallel to the surface of the skin in order to decrease the likelihoodof burns.

West German Patent DE 3,020,789 discloses a electrode which may be usedto deliver medication applied to the body and underneath the electrodesuch that direct current through the electrode will drive the medicationinto the body. An adjustable electrode with a slidable support couplingholds adjustably positioned arms for placement of the electrodes inspaced apart relation. Thus current can be applied to different parts ofthe body and the spacing between the electrodes can be adjusted.International patent application W088/00846 discloses an electrode whichcan be carried on a wrist belt.

Missing from these patents is the fundamental concept of having multipleactive and indifferent elements separated by an insulator wherein thespacing of the elements provides electric field lines located fortransdermally delivering drug to a required depth. The unappreciatedadvantages of such multiple elements are improved power efficiency andthe discovery that the amount of separation of the elements relates tothe penetration depth of the iontophoretic delivery of medication.Improved power efficiency and the relationship of electrode spacing todepth of drug delivery result from placement of the active andindifferent elements against an insulator which sets the spacing andaccordingly the depth of iontophoretic transdermal penetration.

SUMMARY OF THE INVENTION

An iontophoretic electrode array for use in transdermal transport ofionic solutions through mammalian skin has a plurality of iontransmitters for establishing electric field lines in an area and fortransmission of ions along the lines. Each transmitter has a pair oflonger sides and a pair of shorter sides. A plurality of receivers arepositioned for accepting ions flowing along the electric field lines.Each receiver has a pair of longer sides and a pair of shorter sides. Aplurality of shields of a substance to resist the flow of ionsthereacross are located between adjacent transmitters and receiversalong the longer sides thereof. The preferred array has the shieldsinterposed between adjacent transmitters and receivers so that thetransmitters, shields and receivers are arranged in at least a sequenceof transmitter, shield, receiver, shield.

The aspect ratio of the longer to the shorter sides of the respectivetransmitters and receivers is in the preferred embodiments greater thanone and one half. The aspect ratio of the longer to the shorter sides ofthe respective transmitters and receivers is most preferably in therange of four to twenty. The electric field lines emanate substantiallyin one direction transversely across the longer sides of thetransmitters and the receivers and the electric field lines returnthrough the area to adjacent receivers in directions substantiallyopposite the one direction. The transmitters may have a matrix structurewith space therein to contain ionic medication and the matrix structureis preferably a porous substance. Similarly, the receivers can have amatrix structure with space therein to contain electrolyte and also be aporous substance.

A support for holding a plurality of sequences of transmitters andreceivers separated by interposed shields may be included on the array.The support has current carrying contacts positioned thereon and exposedto connect the transmitters and receivers in circuit with a source ofelectrical power. In addition, the source of electrical power ispreferably carried in the support.

In one form of the array the transmitters and receivers are rectangularplate like in shape with a pair of opposed parallel major surfaces boundby sides set perpendicular thereto and a first set of current carryingcontacts are connected in circuit with the source of electrical powerand are exposed to connect with one of the sides of each of thetransmitters. Similarly, the support has a second set of currentcarrying contacts positioned thereon and exposed to connect one of thesides of each of the receivers in circuit with the source of electricalpower. The first and second sets of the contacts are mounted on thesupport in spaced apart relation relative to each other and are locatedon a face thereof. The first set of contacts connected to thetransmitters are arranged in circuit for passing electrons between thesource of electrical power to the transmitters, and the second set ofcontacts connected to the receivers are arranged in circuit for passingelectrons between the receivers and the power sources so that there iscurrent flow from the source of electrical power to the transmitters andthere is current flow from the receivers to the source of electricalpower when ions flow between the sides of the transmitters opposite thefirst set of contacts and the adjacent sides of the receivers oppositethe second set of contacts through the skin. The support may includerecesses so that each shield may extend beyond the face thereon into onerecess.

The array may be used to deliver ionic medication by iontophoresis in apreferred method including establishing an electric field having linesof energy between a plurality of first conductors of ions and aplurality of second conductors of ions. The method has the next step ofpassing ions along the energy lines of the electric field from the firstto the second conductors and through a resistive medium. Thereafter themethod includes restricting the flow of ions to paths between adjacentfirst and second conductors defined by the energy lines of the electricfield. The method has the step of positioning the first conductorsrelative to the second conductors so that the energy lines emanatetherefrom substantially in one direction return to the adjacent secondconductors in another direction opposite the one direction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of the preferred embodiment of anionotophoretic electrode array.

FIG. 2 is an exploded perspective view of an alternate iontophoreticelectrode array.

FIG. 3 is an exploded schematic of an alternate iontophoretic electrodeillustrated in perspective.

FIG. 4 is a graph of current density relative to skin damage forexperiments with a pair of spaced electrodes and with arrays of the typedisclosed in FIGS. 1, 2 or 3.

FIG. 5 is a schematic side elevational view of the pair of spacedelectrodes used to obtain some of the data in the graph of FIG. 4.

DETAIL DESCRIPTION

While this invention is satisfied by embodiments in many differentforms, there is shown in the drawings and will herein be described indetail a preferred embodiment and alternate embodiments of theinvention, with the understanding that the present disclosure is to beconsidered as exemplary of the principles of the invention and is notintended to limit the invention to the embodiments illustrated. Thescope of the invention will be measured by the appended claims and theirequivalents.

An iontophoretic electrode array 10 for placement against the skinduring transdermal transport of ionic solutions through mammalian skinis shown in perspective in FIG. 1. The array 10 has a plurality of iontransmitters 11 for establishing electric field lines 12 in an area Afor placement against the skin and for transmission of ions along thefield lines 12. Each transmitter 11 is configured to have a pair oflonger sides 13 and a pair of shorter sides 14. The array 10 alsoincludes a plurality of receivers 15 in position for accepting ionsflowing along the electric field lines 12 in the area A of the skin. Theshape of each receiver 15 has a pair of longer sides 16 and a pair ofshorter sides 17.

A plurality of shields 18, made of a substance to resist the flow ofions thereacross, are in the array 10. The shields 18 are interposed andlocated between adjacent transmitters 11 and receivers 15 in between thelonger sides 13 and 16 thereof so that the transmitters 11, shields 18and receivers 15 are arranged in at least a sequence of transmitter 11,shield 18, receiver 15, shield 18. The electric field lines 12 aregenerally transverse to the longer sides 13 and 16 as they pass throughthe area A of the skin.

The aspect ratio of the longer sides 13 and 16 to the shorter sides 14and 17 of the respective transmitters 11 and receivers 15 is greaterthan one and one half to one. The preferred range for the aspect ratiobetween four and twenty for the longer sides 13 and 16 to the respectiveshorter sides 14 and 17. The transmitters 11 are made of a materialwhich contains ionic medication. The material is a porous substance withspace therein to contain ionic medication. The material in one form ofthe invention is a hydrogel formulated to include the ionic medication.

The receivers 15 include a material which contains an electrolyte. Thematerial is a porous substance with space therein to contain theelectrolyte. The material in one form of the unit is surrounded by anonconductive gel. U.S. invention is a hydrogel so formulated to includethe electrolyte. The transmitters 11 could alternatively be a matrixstructure with space therein to contain ionic medication and likewisethe receivers 15 could have a matrix structure with space therein tocontain electrolyte. The matrix structure is a porous substance such asPorex brand polymer.

The electrode array has a support 19 for holding a plurality ofsequences of transmitters 11 and receivers 15 separated by interposedshields 18. The support 19 has current carrying contacts 20 positionedthereon and exposed to connect the transmitters 11 and receivers 15 incircuit with a source of electrical power 21. The source of electricalpower 21 is carried in the support 19. The transmitters 11 and receivers15 are rectangular plate like in shape with the pair of longer sides 13and 16 being opposed parallel major surfaces 22 and 23 bound by theshorter sides 14 and 17 perpendicular thereto. In one form of the array10 the support 19 has a first set of current carrying contacts 24connected in circuit with the source of electrical power 21 andpositioned thereon and exposed to connect to the top of each of thetransmitters 11 and wherein the support 19 has a second set of currentcarrying contacts 25 positioned thereon and exposed to connect the topof each of the receivers 15 in circuit with the source of electricalpower 21.

The first and second sets of the contacts 24 and 25 are mounted on thesupport 19 in spaced apart relation relative to each other and arelocated on a face 26 thereof, the first set of contacts 24 connected tothe transmitters 11 are arranged in circuit for passing current from thesource of electrical power 21 to the transmitters 11 and the second setof contacts 25 connected to the receivers 15 are arranged in circuit forreceiving ions from the receivers 15 so that there is current flow fromthe source of electrical power 21 to the transmitters 11 and there iscurrent flow from the receivers 15 to the source of electrical power 21when ions flow between the sides of the transmitters 11 opposite thefirst set of contacts 24 and the adjacent sides of the receivers 15opposite the second set of contacts 25.

The support 19 includes recesses 27 and each shield 18 when assembledextends beyond the face 26 thereon for the first and second contact sets24 and 25 into one recess 27 in the support 19 so that each recess 27locates the transmitters 11 and the first set of contacts 24 in circuitand aligns the receivers 15 and the second set of contacts 25 incircuit.

In FIG. 2 an alternate embodiment of an array 10' has a plurality ofactive members 28, each active member 28 generally rectangular in shapeand having a pair of longer sides 29 opposite each other. Each activemember 28 is made of a material for containing an ionic medicationsolution. A plurality of indifferent members 30 is in the array 10' andeach indifferent member 30 is of generally rectangular shape having apair of longer sides 31 opposite each other. Each indifferent member 30is made of a material for containing an electrolyte solution. Aplurality of insulators 32 is included in the array 10' so eachinsulator 32 has a pair of sides 33 opposite each other and eachinsulator 32 is when assembled placed in side 33 against side 33 contactwith and between the active and indifferent members 28 and 30 formingthe array 10' having at least the sequence of active member 28,insulator 32, indifferent member 30, insulator 32.

The placement of the insulators 32 is such that the longer sides 29 and31 of the generally rectangular active and indifferent members 28 and 30are against the insulators 32 in the sequence. Because of the generallyrectangular shape the aspect ratio of the longer to the shorter sides 34and 35 of the respective active and indifferent members 28 and 30 isgreater than one and one half to one. The aspect ratio of the longersides 29 and 31 to the shorter sides 34 and 35 of the respective activeand indifferent members 28 and 30 is preferably in the range of four totwenty.

The array 10' includes a support 36 for holding a plurality of activemembers 28 and indifferent members 30 separated by interposed insulators32. The support 36 carries contacts 37 positioned thereon and exposed toconnect the active and indifferent members 28 and 30 in circuit with asource of electric power 38. The source of electric power 38 is carriedby the support 36. The longer sides 29 and 31 of the active andindifferent members 28 and 30 are major surfaces 39 and 40 respectively,with each of the members 28 or 30 having a pair of opposed marginalplanes 41 for the active member 28 and 42 for the indifferent member,wherein the planes 41 and 42 are located normal to the major surfaces 39and 40, respectively.

The support 36 has contacts 37 shown in the cut away portion of thesupport 36 of FIG. 2, includes a first set of current carrying contacts24' connected in circuit with the source of electrical power 38 andpositioned on the support 36 and exposed to connect with one of themarginal planes 41 of each of the active members 28. The support 36 hasa second set of current carrying contacts 25' in circuit with the sourceof electrical power 38 and positioned thereon and exposed to connectwith one of the marginal planes 42 of each of the indifferent members30. The first and second sets of the contacts 24' and 25' are mounted onthe support 36 in spaced apart relation relative to each other and arelocated on a face 43 thereof; the first set of contacts 24' connected tothe active members 28 are arranged in circuit for passing current fromthe source of electrical power 38 to the active members 28 and thesecond set of contacts 25' connected to the indifferent members 30arranged in circuit for passing current to the source of electricalpower 38 so that there is current flow from the source of electricalpower to the active members 28 and there is current flow from theindifferent members 30 to the source of electrical power 38 when thereare ions flowing along electrical field lines 12' between active members28 opposite the first set of contacts 24' and indifferent members 30opposite the second set of contacts 25'.

In this form of the array 10' the insulator 32 between each of theactive and indifferent members 28 and 30 respectively, extends beyondthe face 43 thereof for locating the first and second sets of contacts24' and 25' and the support 36 has a plurality of grooves 44 positionedto locate the active members 28 and the first set of contacts 24' incircuit and to align the indifferent members 30 and the second set ofcontacts 25' in circuit when the active and indifferent members 28 and30, insulators 32 and the support 36 are assembled with the majorsurfaces 39 and 40 thereof against the insulators 32 therebetween.

The active members 28 have a matrix structure with space therein tocontain ionic medication and the indifferent members 32 have a matrixstructure with space therein to contain electrolyte. The matrix is aporous polymer of polyethylene.

An alternate iontophoresis electrode 45 shown schematically in FIG. 3,has a plurality of first conductors 46 electrically connected inparallel to a first output 47 of a source of electrical power 48. Eachof the first conductors 46 has an elongate configuration bound onopposite sides and made of a material to readily pass ions thereacross.A plurality of second conductors 49 in the electrode 45 is electricallyconnected in parallel to second output 50 of the source of electricalpower 48. Each of the second conductors 49 has an elongate configurationbound on opposite sides and made of a material to readily pass ionsthereacross. A plurality of insulators 51 of electrically non conductivematerial are in the electrode 45. Each of the insulators 51 has anelongate configuration bound on opposite sides and is made of a materialwhich resists the passage of ions thereacross.

The placement of the insulator 51 material which resists the flow ofions is such that longer sides 52 and 53 of the elongate first andsecond conductors 46 and 49 are against the insulator 51 material whichresists the flow of ions. Because of the generally elongate shape theaspect ratio of the longer sides 52 and 53 to the shorter sides 54 and55 of the respective first and second electrical conductors 46 and 49 isgreater than one and one half to one. The aspect ratio of the longer tothe shorter sides of the respective first and second conductors 46 and49 is preferably in the range of four to twenty. The insulator 51material which resists the flow of ions is interposed between first andsecond conductors 46 and 49 for forming a sandwich construction.

A support 56 is attached to the electrode 45 with a plurality of firstcontacts 57 are positioned in spaced apart relation thereon on a face 58thereof. The first contacts 57 are electrically connected in a firstparallel circuit with the source of electrical power 48 such as abattery and one side 59 of each of the first conductors 46. The support56 has a plurality of second contacts 60 positioned thereon on the face58 thereof and in spaced apart relation. The second contacts 60 areelectrically connected in a second parallel circuit with the source ofelectrical power 59 and one side of each of the second conductors 49.

Although schematically shown within a dashed line, the support 56carries above the face 58 the source of electrical power 48. The support56 includes a reservoir 61 in fluid connection with the first conductors46 and adapted to contain ionic material for transdermal transport bythe first conductors 46. The reservoir 61 is detachably contained on thesupport 56 so that the reservoir 61 can be removed and replaced.

A method of using an iontophoresis electrode 45 for transdermaltransport of an ionic substance is also a part of this invention. Themethod includes the steps of establishing electric field lines 12 ofenergy between the plurality of first conductors 46 of ions and theplurality of second conductors 49 of ions. Then the method includes thestep of passing ions along the energy lines 12 of the electric fieldfrom between the plurality of first to the second conductors 46 and 49and through a semiconductive medium. Thereafter the step includesrestricting the flow of ions to paths between adjacent first and secondconductors 46 and 49 defined by the energy lines 12 of the electricfield. The next step is positioning the first conductors 46 relative tothe second conductors 49 so that the energy lines 12 emanate therefromsubstantially in one direction return to the adjacent second conductors49 in another direction opposite the one direction shown asperpendicular to the skin by arrow B, in FIGS. 1 and 3.

The thickness of the shields 18 or insulators 32 or 51 has a an effectupon how deeply the ionic solution is transported into the skin. For arange of thickness between very thick and very thin shields 18 orinsulators 32 or 51, the electric field lines 12 are still relativelyshort, and hence require relatively low energy to transport the ionicsolution. The electric field lines 12 are sufficiently long, however, sothat the ionic solution is still transported by the electric field lines12 to the epidermis at C and dermis at D for transfer to the vasculatureat E. To some extent, the preferred range extends from 0.01 to 1.0inches or 0.025 to 2.5 centimeters. The most beneficial range is 0.10 to0.62 centimeters.

The stratum corneum at F is essentially unhydrated protein. Since thereare few ions in that material the impedence is high. The granulatedepidermis C is the sight of transformation from the well hydrated basalepidermis C to the unhydrated stratum corneum F. Here the impedencefalls off as the tissue increases in hydration, also because of saltcontent. From the basal epidermis C inward, tissues are well hydrated,and salt solutions isotonic whereby the impedence nears its minimum. Ofcourse, the impedence will vary from person to person and place to placeon any liven person, however, it is known that the impedence is high atthe stratum corneum F gradually decreasing to the granulated epidermiswhere it drops significantly and remains low into and through the basalepidermis C and the dermis D. For very thin shields 18 or insulators 32or 51 in a repeated array 10 or 10' or in an electrode 45 such asdisclosed and described as the embodiments in this specification, theelectric field lines 12 pass through the stratum corneum F and maybe theupper layers of the granulated epidermis C.

These paths are preferred in spite of the high resisitivity or impedenceof the stratum corneum F because the path lengths of the electric fieldlines 12 are short. Since ionic solution flows during transportationalong the electric field lines 12, it can be appreciated that the ionicsolution is transported well into the stratum corneum F then flowsbackup to the receiver. Thus, for very thin insulators, little of themedication reaches the blood stream. Moreover, this approach has thegreatest likelihood to actually short out due to the close spacing ofeither the transmitters and receivers 11 and 15, the active andindifferent members 28 and 30 or the first and second conductors 46 and49.

If the shields 18 or insulators 32 or 51 are very thick, the electricfield lines 12 lengthen as they take the path of least impedence throughthe stratum corneum F and the hydrated tissue C below the stratumcorneum F so they may return through the stratum corneum F to the nextadjacent transmitter 11 or receiver 15, member 28 or 30, or conductor 46or 49, requiring greater levels of energy. This path is most effectivefor transportation of ionic solution to the dermis D, however, itrequires the greatest amount of energy which increases the amount ofskin damage or irritation. An optimum thickness of insulator 32 or 51 orshield 18 exists wherein the field lines are deep enough to cause ionsto reach the bloodstream, and the length of each field line is shortenough to minimize skin irritation.

FIG. 4 is a plot on a graph of the petechial skin damage of anexperiment with iontophoretically transported lidocaine. Along thevertical axis of that graph is shown the damage assessment score whichis the number of petechial (small, punctate, red spots in the skin)observed under the electrode. This axis is linearly divided, thehorizontal axis shows current density necessary in order to transportionic solution. The current density is in microamps per squarecentimeter and the scale is a log scale. The significant data arerepresented by two areas of the plot. The first area of the graph isplotted above the current density range of 25 to 75 microamperes persquare centimeter for a typical iontophoretic electrode of the type inFIG. 5 wherein the active and indifferent members are spaced apart andare of no particular shape as can be seen, damage to the skin begins tooccur at current densities of about 25 microamperes.

The second plot of data in the range of 500 to 1000 microamperes persquare centimeter represent the experiments with the claimed invention.The difference in these data are apparent in that the amount of currentdensity that can be used without damage to the skin is at least tentimes greater than with the schematic showing of an electrode havingactive and indifferent electrodes with a circuit therebetween in FIG. 5.Another way of looking at the data is that current between 100 and 500microamperes per square centimeter can be used to transport drug withoutmeasurable damage using this invention. Note that several data pointsare not typical of that which is expected; those data points show thedifficulty of transportation caused by variations of impedence of theskin. These particular data were obtained during experiments with pigswhere the damage was assessed after each test upon a different area ofthe animal's skin.

The specific material described and the particular configurations of thepreferred and alternate embodiments may be changed without departingfrom the scope of the invention covered by the claims which follow.

What is claimed is:
 1. An electrode array comprising:a plurality ofrectangular active members, each active member having a pair of longsides opposite each other and opposed end surfaces, each of said activemembers made of a material for containing an ionic medication solution;a plurality of rectangular indifferent members each having a pair oflong sides opposite each other and opposed end surfaces, each of saidindifferent members made of a material for containing an electrolytesolution; and a plurality of insulators each having a pair of sidesopposite each other, each of said insulators placed in side against sidecontact with and between the long sides of said active and indifferentmembers which are spaced and parallel to each other forming an arrayhaving at least the sequence of active member, insulator, indifferentmember, insulator.
 2. The electrode array of claim 1 wherein therectangular active members and the rectangular indifferent members havea common aspect ratio.
 3. The electrode array of claim 2 wherein theaspect ratio is greater than one and one half.
 4. The electrode array ofclaim 1 including support means for holding said plurality of activemembers and said indifferent members separated by said interposedinsulators.
 5. The electrode array of claim 4 further including acircuit wherein said support means has current carrying contactspositioned thereon, wherein said contacts connect the active andindifferent members to said circuit includes a source of electric power.6. The electrode array of claim 5 wherein the source of electric poweris a battery and said support means including means for engaging saidbattery.
 7. The electrode array of claim 5 wherein said current carryingcontacts include a first set of current carrying contacts connected incircuit with the source of electrical power and positioned on saidsupport means and exposed to connect with one of the end surfaces ofeach of the active members and a second set of current carrying contactspositioned on said support means and exposed to connect with one of theend surfaces of each of the indifferent members in circuit with thesource of electrical power.
 8. The electrode array of claim 7 whereinthe first and second sets of the contacts are mounted on the supportmeans in spaced apart relation relative to each other and are located ona face thereof, the first set of contacts connected to the activemembers are arranged in circuit for passing current from the source ofelectrical power to the active members and the second set of contactsconnected to the indifferent members are arranged in circuit for passingcurrent to the source of electrical power so that when said electrodearray is placed against mammalian skin there is current flow from thesource of electrical power to the active members and there is currentflow from the indifferent members to the source of electrical power. 9.The electrode array of claim 8 wherein each of said insulators betweeneach of the active and indifferent members extends beyond the face andthe support means has a plurality of grooves positioned to locate theactive members and the first set of contacts in circuit and to align theindifferent members and the second set of contacts in circuit.
 10. Theelectrode array of claim 1 wherein the active members have a matrixstructure with space therein adapted for receiving ionic medication andthe indifferent members have a matrix structure with space thereinadapted for receiving electrolyte.
 11. The electrode array of claim 10wherein the matrix structure is a porous polymer.
 12. An iontophoresiselectrode comprising:a plurality of first ionic conductors electricallyconnected in parallel for connection to a first output of a source ofelectrical power, each of the first conductors having an elongateconfiguration including a plurality of elongate sides and made of amaterial to readily pass ions thereacross; a plurality of second ionicconductors electrically connected in parallel for connection to a secondoutput of the source of electrical power, each of the second conductorshaving an elongate configuration including a plurality of elongate sidesand made of a material to readily pass ions thereacross; a plurality ofinsulators of electrically non-conductive material, each of theinsulators having an elongate configuration including a plurality ofelongate sides and made of a material which resists the passage of ionsthereacross, the insulators each interposed between said first andsecond conductors for forming a sandwich construction; and a supporthaving a plurality of first contacts positioned thereon on a facethereof and in spaced apart relation, the first contacts electricallyconnected in a first parallel circuit with one elongate side of each ofthe first conductors, the support having a plurality of second contactspositioned thereon on the face thereof and in spaced apart relation, thesecond contacts electrically connected in a second parallel circuit withone elongate side of each of the second conductors, the supportincluding means for engaging a source of electrical power to said firstand second parallel circuits.
 13. The electrode of claim 12 wherein anaspect ratio of the elongate first conductors is greater than one andone half.
 14. The electrode of claim 12 wherein an aspect ratio of theelongate second conductors is greater than one and one half.
 15. Theelectrode of claim 12 wherein the support includes reservoir means forfluid communication with the first conductors and adapted to containionic material for transdermal transport by the first conductors. 16.The electrode of claim 15 wherein said support includes means fordetachably retaining said reservoir means so that said reservoir meanscan be removed and replaced.